Microelectronic integrated circuits, such as microprocessors, comprise literally hundreds of millions of transistors. The speed of the integrated circuits is primarily dependent on the performance of these transistors. Thus, the industry has developed unique structures, such as non-planar transistors, to improve performance.
Alternative channel materials such as Germanium (Ge) enable higher performance transistors. These materials are integrated with a silicon substrate to be most useful. The integration scheme should allow selection of transistor material type for each transistor in the design. Heteroepitaxy of germanium on silicon is achieved today using wafer-scale or large area blanket growth using thick buffer layers of intermediate SiGe composition to accommodate the lattice mismatch defects. The thick buffer makes it difficult to form small Ge islands mixed with Si for use in a single circuit. This approach also suffers from relatively high defect density compared to conventional Si wafers.